As mentioned in last article, dedicated bearer is meant for
specific QoS and always associated with default bearer (which
provide initial/basic PDN connectivity). Dedicated bearer setup is
always initiated by EPC. EPC triggers dedicated bearer setup due
to incoming packet connection (call) or due to ESM request sent by
UE.

Below is a end-to-end signaling diagram for dedicated bearer setup.

UE

eNB

MME

SGW

PGW

Default EPS bearer is assumed to be present.UE require bearer with specific QoS (mostly different than that provided by default bearer). UE in RRC-Connected, EMM-Registered, ECM-Connected state.EPS bearer 23.401:4.7.2Bearers/QoS 36.300:13

eNB App/RRM (Admission control & Scheduling) plays an important part here. RRM comes out with Radio QoS out of given EPS QoS based on current radio load situation and invokes RRC Reconfig procedure.RRM functions 36.300:16.1